1. Field of the Invention
The present invention relates to the technical field of ultrasonic nebulizers and, more particularly, to an ultrasonic nebulizer for producing high-volume sub-micron droplets.
2. Description of Related Art
An ultrasonic nebulizer uses an oscillation signal to drive a piezoelectric ceramic oscillator for producing mechanical vibration. The vibration energy is coupled to a liquid to be nebulized for producing capillary waves thereon and droplets. The ultrasonic nebulizer can be used for medication or producing droplet applications. Generally an oscillation frequency of a conventional ultrasonic nebulizer is 1.6 MHz or 2.4 MHz. As shown in FIG. 1, the average diameter of droplets produced by a conventional ultrasonic nebulizer at 1.6 MHz and 2.4 MHz are 2.3 μm and 1.7 μm respectively. The droplets with a diameter of 2.3 μm and 1.7 μm are too large for treatment of an alveolus. In general, the droplets with a diameter large than 1.0 μm are easily absorbed by a bronchus or bronchioles before entering the alveolus. On the contrary, most droplets with a diameter less than 1.0 μm easily pass through the bronchus or bronchioles and are absorbed by the alveolus. FIG. 1 shows that the total quantity of droplets with a diameter less than 1.0 μm is very little for a conventional nebulizer with a 2.4 MHZ oscillation frequency, and therefore the total volume of the droplets entering the alveolus is also very little and is not suitable for treating an alveolus. However, if the oscillation frequency can be changed to 5 MHz, then the volume of the droplets with a diameter less than 1.0 μm can be dramatically increased for treating the alveolus. Therefore, there is a need to have a novel design for a nebulizer that can mitigate and/or obviate the aforementioned problems.